Weird Trailer Park Light Problem

[WCCoffey]

04 2500 4wd w/ factory towing package

So I'm kinda stumped. I have been searching everywhere for a wiring diagram of the trailer brake system on my truck and haven't found squat.

All lights on truck and trailer work properly except the trailer parking lights.

I checked the fuse for it, its fine, and has 12volts at the fuse. So I checked EVERY fuse... everything is ok..

After messing with it and messing with it I looked up underneith the truck and found a second 7 pin plug above the spare tire. I have no idea why this is there.. It comes out of the trailer harness that goes up to the front of the truck and then plugs into a connector that goes right back into the same harness. This all looks like factory stuff and looks like its never been unplugged, its all coated in dirt.

I unplugged that connector and plugged it into the back of the trailer connector that mounts on the trailer hitch... and now the parking lights work..

BUT the other connector that is supposed to be plugged into it has no 12v at the pin for the parking lights...

The park lights were working about 2 months ago and last month I got a ticket for no park lights on the trailer... So of course I'm waiting till the last second to fix it... I didn't think it would be a big deal..

Do any of you know why the second connector is up there and what its for? I'm going to leave it hooked up for now because I have to drive at night but I need to figure this out ASAP as I'm going out of town tomorrow and will be driving at night (with my trailer)

[rd05lly]

It is for a in bed hook up.

[WCCoffey]

that makes sense, but why would it be plugged back into the harness? Hmmm...

[rd05lly]

It should have been rolled up above fuel tank.

[Hook'em_Horns!]

Pull your truck's 7-pin plug/harness from the mounting door on the hitch/bumper (it's a plug in a plug). Once removed, open up the plug head and check for loose terminals inside, specifically #3 and #1 posts.



If tight, meter it to check for bad contact blade in plug or for any corrosion on the plug's mount/door there at the bumper/hitch.

[WCCoffey]

There is no 12v in the wire.

[Hook'em_Horns!]

If the secondary harness (for GN/5th wheel in-bed plug) works but the primary doesn’t, and you’ve opened up the plug head to find no 12v there, then follow the dead circuit on the primary back till you find the live 12v.

Since the 2nd harness is live, I would think your problem lies in the primary plug head itself. You did open it up to check? Not just meter the pin on the output? Damage to the primary harness from the plug to the connector would be hard to miss I would think.

[WCCoffey]

So these 2 connecters are infact the same circuit?

I pierced the wire to check voltage.. There is no physical damage to the harness.. I need to pull the bed off to check the fuel pick up and fuel lines for a weird no start condition (prime it and it will start) when the fuel level gets below 1/4 tank. I guess I'll just cut the harness open then and inspect it.

[Hook'em_Horns!]

Originally Posted by WCCoffey

So these 2 connecters are infact the same circuit?

Yes. They both tie in to the same feed from the front. Check for continuity on the primary harness section going to the hitch. Is there a problem where that section ties in?

[WCCoffey]

I dont know where the 2 circuits join each other so I'm gonna have to peal back the harness. I am going to leave it the way it is till I get back from my trip..


Thanks for the help guys.